Gasification medium (GM), which by means of gasification-medium nozzles (GM nozzles) is injected into particle-loaded gasification spaces of fixed-bed, fluidized-bed or entrained-bed gasifiers, frequently consists of a vapor/oxygen mixture (GM mixture). Beside pure vapor/oxygen mixtures other GM mixtures are also used, e.g. by admixing air, CO2 and other usable gases. The GM nozzles are designed both as externally cooled and as uncooled one-component nozzles. From the multitude of gasification processes, the British Gas/Lurgi slag bath gasification process (BGL gasifier) should subsequently be selected, by means of which the fact of injection can be represented particularly clearly in its complexity.
A vapor/oxygen mixture with a mixing ratio of about 1 kg vapor/Nm3 oxygen is injected into the BGL gasifier. The GM nozzles are inclined downwards against the horizontal. The GM jet leaving the GM nozzles is directed onto the surface of the slag bath in the bottom portion of the BGL gasifier. When operated as specified, the GM mixture reacts with coke carbon particles and other oxidizable components present in the reaction space in direct vicinity in front of the nozzle orifice and releases heat due to combustion reactions. In the developing air-blast tuyere of the BGL gasifier, temperatures up to more than 2000° C. are usually obtained. At these temperatures, the slag is present as low-viscosity liquid.
The nozzle head protruding into the reaction space of the BGL gasifier is cooled intensively to avoid slag accretions and to protect against metal oxidation. The outer contours of the GM nozzles are designed to be compact and save surface area, in order to keep working surfaces for slag and the introduction of heat into the GM nozzles as low as possible.
The GM nozzles are designed as one-component nozzles. To definitely prevent slag or carbonaceous components from entering the GM nozzle through the cylindrical nozzle orifice and from impeding or blocking the nozzle exit, the gasification medium (GM) is blown out from the nozzle orifice at rather high speed. Under nominal load of the BGL gasifier, the GM exit rate is about 60 to 180 m/s. The higher the GM exit rate, the higher the risk of particles being sucked back into the GM nozzle. The nozzle orifices are clogged and finally block the exit of gasification medium. Disturbed nozzles are detected by measuring a low flame intensity and a decrease in the amount of gasification medium reaching the nozzle. Largely clogged or even blocked, so-called “black” nozzles must be shut off for safety reasons. This leads to performance losses up to the premature shut-down of the BGL gasifier. Experience has shown that frequently a plurality of nozzles go “black” at the same time or in quick succession, must be shut off, and thus necessitate the shut-down of the BGL gasifier before long. To fortify the GM nozzles, the BGL gasifier must be cooled and drained. This leads to long downtimes with considerable losses of output and high maintenance costs. In practical operation, the BGL must repeatedly be shut off due to the ingress of slag and carbonaceous material into the GM nozzles, in particular under unstable operating conditions and during start-up processes.
An essential safety criterion for the operation of the BGL gasifier is the assurance of an undisturbed, regular outflow of the gasification medium from the GM nozzles, which can only be ensured by absolute cleanliness of the inner nozzle contour of the GM nozzle in direct vicinity of the nozzle orifice. An undisturbed jet exit generally is accompanied by the undisturbed and uniform formation of a flame in front of the nozzle. An undisturbed, free formation of a jet is the best guarantee that the oxygen discharged reacts directly in front of the nozzle, is not deflected and does not get into colder regions of the BGL gasifier or to the ceramic brick lining unreacted. So far, there are no solutions to this problem.
What turns out to be particularly critical is the increased failure frequency of the GM nozzles during the gasification of heterogeneous waste substance mixtures in the BGL gasifier, the gasification and slag flow behavior of such mixtures being characterized by particularly strong irregularities. The following causes should be mentioned: extremely quickly variable slag viscosities and rapidly changing slag bath levels due to strong variations in the ash content and quality, very high and greatly varying temperatures in front of the nozzles due to the high and varying GM/coke ratio of the generally highly volatile waste substances, strong pressure pulsations in the air-blast tuyere in front of the nozzles.
The problems of the injection of gasification medium into particle-loaded gasification spaces, which were described with reference to the example of the BGL gasifier, similarly exist also for other gasification processes, such as the HTW fluidized-bed gasification. To solve these problems, very expensive two-component nozzles are used, which restrict the operational flexibility. The susceptibility to failure can likewise not be decreased to a sufficient extent.
As a result of the disadvantages of the prior art, it is the object of the invention to ensure a stable and uninterrupted supply of gasification medium (GM) into particle-loaded gasification spaces under all operating conditions and to ensure an undisturbed, uniform and intensive formation of a flame in front of the GM nozzles, even when using extremely hetereogeneous feedstocks, to avoid the clogging of GM nozzles, the shut-down of clogged GM nozzles and thus, in the final analysis, the premature shut-down of the gasifier.